Prognostic Role of Cardiopulmonary Exercise Testing in Clinical Practice

A nomogram to distinguish noncardiac chest pain based on cardiopulmonary exercise testing in cardiology clinic

BACKGROUND

Psychological disorders, such as anxiety and depression, are considered to be one of the causes of noncardiac chest pain (NCCP). And these patients can be challenging to differentiate from coronary artery disease (CAD), leading to a considerable number of patients still undergoing angiography. We aim to develop a practical prediction model and nomogram using cardiopulmonary exercise testing (CPET), to help identify these patients.

METHODS

1,531 eligible patients' electronic medical record data were obtained from Guangdong Provincial People's Hospital. They were randomly divided into a training dataset (N = 918) and a testing dataset (N = 613) at a ratio of 6:4, and 595 cases without missing data were also selected from testing dataset to form a complete dataset. The training set is used to build the model, and the testing set and the complete set are used for internal validation. Eight machine learning (ML) methods are used to build the model and the best model is finally adopted.

RESULTS

The model built by logistic regression performed the best, and among the 29 parameters, six parameters were determined to be valuable parameters for establishing the diagnostic equation and nomogram. The nomogram showed favorable calibration and discrimination with an area under the receiver operating characteristic curve (AUC) of 0.857 in the training set, 0.851 in the testing set, and 0.848 in the complete set. Meanwhile, decision curve analysis demonstrated the clinical utility of the nomogram.

CONCLUSIONS

A nomogram using CPET to distinguish anxiety/depression from CAD was developed. It may optimize the disease management and improve patient prognosis.

End-tidal oxygen partial pressure is a strong prognostic predictive factor in patients with cardiac disease

BACKGROUND

Cardiopulmonary exercise testing (CPET) variables represent central and peripheral factors and combined factors in the pathology of patients with cardiac disease. The difference in end-tidal oxygen partial pressure from resting to anaerobic threshold (ΔPETO2 ) may represent predominantly peripheral factors. This study aimed to verify the prognostic significance of ΔPETO2 for major adverse cardiac and cerebrovascular events (MACCE) in cardiac patients, including comparison with the minute ventilation-carbon dioxide production relationship (VE/VCO2 slope), and peak oxygen uptake (VO2 ).

METHODS

In total, 185 patients with cardiac disease who underwent CPET were consecutively enroled in this retrospective study. The primary endpoint was 3-year MACCE. The ability of ΔPETO2 , VE/VCO2 slope, and peak VO2 to predict MACCE was examined.

RESULTS

Optimal cut-off values for predicting MACCE were 2.0 mmHg for ΔPETO2 (area under the curve [AUC]: 0.829), 29.8 for VE/VCO2 slope (AUC: 0.734), and 19.0 mL/min/kg for peak VO2 (AUC: 0.755). The AUC of ΔPETO2 was higher than those of VE/VCO2 slope and peak VO2 . The MACCE-free survival rate was significantly lower in the ΔPETO2  ≤ 2.0 group versus the ΔPETO2  > 2.0 group (44.4% vs. 91.2%, p < 0.001). ΔPETO2  ≤ 2.0 was an independent predictor of MACCE after adjustment for age and VE/VCO2 slope (hazard ratio [HR], 7.28; p < 0.001) and after adjustment for age and peak VO2 (HR, 6.52; p < 0.001).

CONCLUSION

ΔPETO2 was a strong predictor of MACCE independent of and superior to VE/VCO2 slope and peak VO2 in patients with cardiac disease.

Time of the low-level cardiopulmonary exercise test does not affect the evaluation of acute myocardial infarction in stable status

Introduction

Cardiopulmonary exercise test (CPET) provides the means to evaluate the cardiopulmonary function and guide cardiac rehabilitation. The performance of acute myocardial infarction (AMI) patients at different times is different on CPET.

Materials and methods

This was a cross-sectional study. Patients diagnosed as AMI in stable status were included and performed the low- level CPET (RAMP 10W). CPET variables at different times were compared among four groups.

Results

Sixty and one patients with AMI conducted the low-level CPET from 3 to 15 days after AMI. Patients were stratified according to quartiles of CPET's time: 5 in 3-6 days group, 34 in 7-9 days group, 14 in 10-12 days group, 8 in 13-15 days group. Only VO2/HR at rest showed statistically different among the four groups.VO2/HR at rest in 3-6 days group and 10-12 days group were higher than in 13-15 days group (3.4 ± 0.85, 3.18 ± 0.78 vs. 2.50 ± 0.49 ml/beat, p < 0.05). Patients with complete revascularization had higher peak heart rate and blood pressure product and peak breathing reserve (BR), and lower Borg score compared with incomplete revascularization. And patients with LVEF >50% had higher peak BR compared with LVEF 40-50%.

Conclusion

It was safe and efficient to conduct the low-level CPET in stable AMI patients 3 days after onset. Time was not an effector on cardiopulmonary function and exercise capacity and prognosis in AMI during CPET. Complete revascularization and normal LVEF should be good for exercise test in AMI.

The double anaerobic threshold in heart failure: MECKI score database overview

AIMS

In heart failure (HF), anaerobic threshold (AT) may be indeterminable but its value held a relevant prognostic role. AT is evaluated joining three methods: V-slope, ventilatory equivalent, and end-tidal methods. The possible non-concordance between the V-slope (met AT) and the other two methods (vent AT) has been highlighted in healthy individuals and named double threshold (DT).

METHODS AND RESULTS

We reanalysed 1075 cardiopulmonary exercise tests of HF patients recruited in the Metabolic Exercise test data combined with Cardiac and Kidney Indexes (MECKI) score database. We identified DT in 43% of cases. Met AT precedes vent AT being met-ventΔVO₂ 221 (interquartile range: 129-319) mL/min. Peak VO₂ , 1307 ± 485 vs. 1343 ± 446 mL/min (63 ± 17 vs. 63 ± 17 percentage of predicted), was similar between DT+ and DT- patients. Differently, DT+ showed a lower ventilatory vs. carbon dioxide production (VE/VCO₂ ) slope (29.6 ± 6.1 vs. 31.0 ± 6.3), a lower peak exercise end-tidal oxygen tension (PetO₂ ) 115.3 (111.5-118.9) vs. 116.4 (112.4-120.2) mmHg, and a higher carbon dioxide tension (PetCO₂ ) 34.2 (30.9-37.1) vs. 32.4 (28.7-35.5) mmHg. Vent AT showed a significant higher VO₂ , 957 ± 318 vs. 719 ± 252 mL/min, VCO₂ , 939 ± 319 vs. 627 ± 226 mL/min, ventilation, 31.0 ± 8.3 vs. 22.5 ± 6.3 L/min, respiratory exchange ratio, 0.98 ± 0.08 vs. 0.87 ± 0.07, PetO₂ , 108 (104-112) vs. 105 (101-109) mmHg, PetCO₂ , 37 (34-40) vs. 36 (33-39) mmHg, and VE/VO₂ ratio, 33.5 ± 6.7 vs. 32.6 ± 6.9, but lower VE/VCO₂ ratio, 33 (30-37) vs. 36 (32-41), compared with met AT. At 2 year survival by Kaplan-Meier analysis, even adjusted for confounders, DT resulted not associated with survival.

CONCLUSIONS

Double threshold is frequently observed in HF patients. DT+ is associated to a decreased ventilatory response during exercise.

Exercise Capacity and Cardiorespiratory Fitness in Children with Congenital Heart Diseases: A Proposal for an Adapted NYHA Classification

OBJECTIVE

To propose and evaluate an adapted NYHA classification for children with congenital heart disease (CHD) as a feasible clinical tool for classifying patients' fitness, cardiorespiratory efficiency and functional limitations during their ordinary daily activities, which are also characterized by vigorous and competitive physical exercise among peers.

METHODS

This cross-sectional investigation analyzed 332 patients (13.1 ± 3.01 y/o) who underwent surgical repair of CHD and performed Cardiopulmonary Exercise Testing (CPET). Patients were divided into NYHA class I, IIA and IIB by specific questioning regarding functional limitation and performance compared to peers and at strenuous intensity. Class IIA was characterized by slight exercise limitation only for strenuous/competitive activities, whereas IIB for already ordinary physical activities. These NYHA classes were compared with maximal CPET on treadmill.

RESULTS

Patients' exercise capacity (exercise time, METs), aerobic capacity (VO2peak) and chronotropic response were found progressively impaired when NYHA class I was compared with IIA and IIB. Indeed, ventilatory-perfusion mismatch (PETCO2, VE/VCO2) significantly worsened from NYHA class I to IIA, while no difference was found between IIA and IIB.

CONCLUSION

This adapted NYHA-CHD classification could allow regular functional evaluations and accurate assessments by clinicians, leading to facilitated clinical management and timely medical interventions.

Listing Criteria for Heart Transplant: Role of Cardiopulmonary Exercise Test and of Prognostic Scores

Patients with advanced heart failure (AdHF) have a reduced quality of life and poor prognosis. A heart transplant (HT) is an effective treatment for such patients. Still, because of a shortage of donor organs, the final decision to place a patient without contraindications on the HT waiting list is based on detailed risk-benefit analysis. Cardiopulmonary exercise tests (CPETs) play a pivotal role in guiding selection in patients with AdHF considered for an HT. Furthermore, several validated multivariable predicting scores obtained through various techniques, including the CPETs, are available and part of the decision-making process for HT listing.

Measures of excess [Formula: see text]CO2 and recovery [Formula: see text]CO2 as indices of performance fatigability during exercise: a pilot study

BACKGROUND

The severity of performance fatigability and the capacity to recover from activity are profoundly influenced by skeletal muscle energetics, specifically the ability to buffer fatigue-inducing ions produced from anaerobic metabolism. Mechanisms responsible for buffering these ions result in the production of excess carbon dioxide (CO2) that can be measured as expired CO2 ([Formula: see text]CO2) during cardiopulmonary exercise testing (CPET). The primary objective of this study was to assess the feasibility of select assessment procedures for use in planning and carrying out interventional studies, which are larger interventional studies investigating the relationships between CO2 expiration, measured during and after both CPET and submaximal exercise testing, and performance fatigability.

METHODS

Cross-sectional, pilot study design. Seven healthy subjects (30.7±5.1 years; 5 females) completed a peak CPET and constant work-rate test (CWRT) on separate days, each followed by a 10-min recovery then 10-min walk test. Oxygen consumption ([Formula: see text]O2) and [Formula: see text]CO2 on- and off-kinetics (transition constant and oxidative response index), excess-[Formula: see text]CO2, and performance fatigability severity scores (PFSS) were measured. Data were analyzed using regression analyses.

RESULTS

All subjects that met the inclusion/exclusion criteria and consented to participate in the study completed all exercise testing sessions with no adverse events. All testing procedures were carried out successfully and outcome measures were obtained, as intended, without adverse events. Excess-[Formula: see text]CO2 accounted for 61% of the variability in performance fatigability as measured by [Formula: see text]O2 on-kinetic ORI (ml/s) (R2=0.614; y = 8.474x - 4.379, 95% CI [0.748, 16.200]) and 62% of the variability as measured by PFSS (R2=0.619; y =  - 0.096x + 1.267, 95% CI [-0.183, -0.009]). During CPET, [Formula: see text]CO2 -off ORI accounted for 70% (R2=0.695; y = 1.390x - 11.984, 95% CI [0.331, 2.449]) and [Formula: see text]CO2 -off Kt for 73% of the variability in performance fatigability measured by [Formula: see text]O2 on-kinetic ORI (ml/s) (R2=0.730; y = 1.818x - 13.639, 95% CI [0.548, 3.087]).

CONCLUSION

The findings of this study suggest that utilizing [Formula: see text]CO2 measures may be a viable and useful addition or alternative to [Formula: see text]O2 measures, warranting further study. While the current protocol appeared to be satisfactory, for obtaining select cardiopulmonary and performance fatigability measures as intended, modifications to the current protocol to consider in subsequent, larger studies may include use of an alternate mode or measure to enable control of work rate constancy during performance fatigability testing following initial CPET.

Evidence of a double anaerobic threshold in healthy subjects

AIMS

The anaerobic threshold (AT) is an important cardiopulmonary exercise test (CPET) parameter both in healthy and in patients. It is normally determined with three approaches: V-slope method, ventilatory equivalent method, and end-tidal method. The finding of different AT values with these methods is only anecdotic. We defined the presence of a double threshold (DT) when a ΔVO2 > 15 mL/min was observed between the V-slope method (met AT) and the other two methods (vent AT). The aim was to identify whether there is a DT in healthy subjects.

METHODS AND RESULTS

We retrospectively analysed 476 healthy subjects who performed CPET in our laboratory between 2009 and 2018. We identified 51 subjects with a DT (11% of cases). Cardiopulmonary exercise test data at rest and during the exercise were not different in subjects with DT compared to those without. Met AT always preceded vent AT. Compared to subjects without DT, those with DT showed at met AT lower carbon dioxide output (VCO2), end-tidal carbon dioxide tension (PetCO2) and respiratory exchange ratio (RER), and higher ventilatory equivalent for carbon dioxide (VE/VCO2). Compared to met AT, vent AT showed a higher oxygen uptake (VO2), VCO2, ventilation, respiratory rate, RER, work rate, and PetCO2 but a lower VE/VCO2 and end-tidal oxygen tension. Finally, subjects with DT showed a higher VO2 increase during the isocapnic buffering period.

CONCLUSION

Double threshold was present in healthy subjects. The presence of DT does not influence peak exercise performance, but it is associated with a delayed before acidosis-induced hyperventilation.

Exercise capacity in patients with repaired Tetralogy of Fallot aged 6 to 63 years

OBJECTIVES

This study aimed to provide a perspective for the interpretation of exercise capacity (peakVO₂) in patients with repaired Tetralogy of Fallot (patients with rTOF) by describing the course of peakVO₂ from patients aged 6-63 years.

METHODS

A retrospective study was performed between September 2001 and December 2016 in the German Heart Centre Munich, Germany, and in the University Medical Centre Groningen, the Netherlands. A total of 1175 cardiopulmonary exercise tests (CPETs) were collected from 586 patients with rTOF, 46% female. Maximal exertion was verified using a respiratory exchange ratio ≥1.00. PeakVO₂ was modelled using time-dependent multilevel models for repeated measurements (n=889 in 300 patients), and compared with subject-specific reference values calculated by the models of Bongers et al and Mylius et al. RESULTS: The peakVO₂ of patients with rTOF was reduced at all ages. At the age of 6, the peakVO₂ was 614 mL/min (70% of predicted (95% CI 67 to 73)). The reduced increase in peakVO₂ during adolescence resulted in a significant lower maximum peakVO₂ of 1209 mL/min at 25 years (65% predicted, p<0.001). A linear decline after 25 years was observed in patients and references, although patients showed an accelerated decline, with a -0.24% point of predicted (95% CI 0.11 to 0.38) per year without differences between sexes (p=0.263).

CONCLUSIONS

This study provides a context for peakVO₂ across ages in patients with rTOF under contemporary treatment strategies. It showed that the reduction in peakVO₂ originates from childhood and declines over time. Sex differences in patients with rTOF were similar to natural existing sex differences.

Effect of pulmonary hypertension on exercise tolerance in patients with COPD: a prognostic systematic review and meta-analysis

Background

Pulmonary hypertension (PH) is a frequent complication in patients with COPD.

Objective

To determine if, in patients with COPD, the presence of PH decreases exercise tolerance.

Methods

We included studies that analysed exercise tolerance using a cardiopulmonary exercise test (CPET) in patients with COPD with PH (COPD-PH) and without PH (COPD-nonPH). Two independent reviewers analysed the studies, extracted the data and assessed the quality of the evidence.

Results

Of the 4915 articles initially identified, seven reported 257 patients with COPD-PH and 404 patients with COPD-nonPH. The COPD-PH group showed differences in peak oxygen consumption (V′_O2peak), −3.09 mL·kg⁻¹·min⁻¹ (95% CI −4.74 to −1.43, p=0.0003); maximum workload (W_max), −20.5 W (95% CI −34.4 to −6.5, p=0.004); and oxygen pulse (O₂ pulse), −1.24 mL·beat⁻¹ (95% CI −2.40 to −0.09, p=0.03), in comparison to the group with COPD-nonPH. If we excluded studies with lung transplant candidates, the sensitivity analyses showed even bigger differences: V′_O2, −4.26 mL·min⁻¹·kg⁻¹ (95% CI −5.50 to −3.02 mL·kg⁻¹·min⁻¹, p<0.00001); W_max, −26.6 W (95% CI −32.1 to −21.1 W, p<0.00001); and O₂ pulse, −2.04 mL·beat⁻¹ (95% CI −2.92 to −1.15 mL·beat⁻¹, p<0.0001).

Conclusion

Exercise tolerance was significantly lower in patients with COPD-PH than in patients with COPD-nonPH, particularly in nontransplant candidates.

The V′_O2peak, Wmax and O₂ pulse values were significantly lower in patients with COPD-PH than in patients with COPD-nonPH, particularly in nontransplant candidateshttps://bit.ly/3s5dtJ9

The Effect of a High-Intensity PrO2Fit Inspiratory Muscle Training Intervention on Physiological and Psychological Health in Adults with Bronchiectasis: A Mixed-Methods Study

Bronchiectasis is characterised by airflow obstruction and hyperinflation resulting in respiratory muscle weakness, and decreased exercise capacity. Inspiratory muscle training (IMT) is potentially an alternative treatment strategy to enhance respiratory muscle strength and endurance. Therefore, the aim was to investigate the effects of IMT on those with bronchiectasis. Eighteen participants (10 bronchiectasis) took part in an eight-week, three times a week IMT programme at 80% sustained maximal inspiratory pressure (SMIP). Lung function, respiratory muscle strength and endurance, exercise capacity, physical activity and self-determination theory measures were taken. Participants also took part in a semi-structured interview to assess their perceptions and experience of an IMT intervention. After eight weeks of IMT, bronchiectasis and healthy participants exhibited significant increases in MIP (27% vs. 32%, respectively), SMIP (16% vs. 17%, respectively) and inspiratory duration (36% vs. 30%, respectively). Healthy participants exhibited further improvements in peak expiratory flow and maximal oxygen consumption. Bronchiectasis participants reported high levels of perceived competence and motivation, reporting higher adherence and improved physical ability. Eight weeks of IMT increased inspiratory muscle strength and endurance in those with bronchiectasis. IMT also had a positive effect on perceived competency and autonomy, with bronchiectasis participants reporting improved physical ability and motivation, and high adherence.

The Interrelationship between Ventilatory Inefficiency and Left Ventricular Ejection Fraction in Terms of Cardiovascular Outcomes in Heart Failure Outpatients

The relationship between left ventricular ejection fraction (LVEF) and cardiovascular (CV) outcome is documented in patients with low LVEF. Ventilatory inefficiency is an important prognostic predictor. We hypothesized that the presence of ventilatory inefficiency influences the prognostic predictability of LVEF in heart failure (HF) outpatients. In total, 169 HF outpatients underwent the cardiopulmonary exercise test (CPET) and were followed up for a median of 9.25 years. Subjects were divided into five groups of similar size according to baseline LVEF (≤39%, 40-58%, 59-68%, 69-74%, and ≥75%). The primary endpoints were CV mortality and first HF hospitalization. The Cox proportional hazard model was used for simple and multiple regression analyses to evaluate the interrelationship between LVEF and ventilatory inefficiency (ventilatory equivalent for carbon dioxide (VE/VCO2) at anaerobic threshold (AT) >34.3, optimized cut-point). Only LVEF and VE/VCO2 at AT were significant predictors of major CV events. The lower LVEF subgroup (LVEF ≤ 39%) was associated with an increased risk of CV events, relative to the LVEF ≥75% subgroup, except for patients with ventilatory inefficiency (p = 0.400). In conclusion, ventilatory inefficiency influenced the prognostic predictability of LVEF in reduced LVEF outpatients. Ventilatory inefficiency can be used as a therapeutic target in HF management.

Cardiorespiratory Performance and Acute Effect of High-intensity Exercise on Lipid Profile in Hypertensive Sedentary Older Adults with and without Diabetes Mellitus

PURPOSE

The aim of this study was to verify if the association of hypertension and diabetes mellitus could lead to the differences on cardiorespiratory fitness and lipid profile in older adults.

METHODS

40 older adults were divided into two groups: Hypertensive (HTN) and Hypertensive-diabetic (HTN + T2DM). Maximum exercise test on a treadmill was conducted. Lipid profiles assessment was conducted before and after exercise. The cardiorespiratory fitness (CRF) variables were peak oxygen consumption (VO_2peak), time to reach peak oxygen consumption (TVO_2peak), carbon dioxide ventilatory equivalent (VE/VCO₂) and carbon dioxide production (VCO₂). To test intergroup and intragroup analyses independent and paired t-tests were used before and after acute exercise. Multiple linear regression was performed to test the influence of coexistence of HTN and T2DM on CRF.

RESULTS

CRF measures such as VO_2peak (β = -3.90), VCO₂ (β = -3.87) and TVO_2peak (β= -115.79) were significantly (p-value <0.01) lower in HTN + T2DM group. After acute exercise, there was an increase in the levels of lipid profile variables, however without differences between groups.

CONCLUSION

HTN + T2DM older adults had poorer CRF. Acute changes in lipemia were similar in both groups.

Performance of cardiopulmonary exercise testing for the prediction of post-operative complications in non cardiopulmonary surgery: A systematic review

INTRODUCTION

Cardiopulmonary exercise testing (CPET) is widely used within the United Kingdom for preoperative risk stratification. Despite this, CPET's performance in predicting adverse events has not been systematically evaluated within the framework of classifier performance.

METHODS

After prospective registration on PROSPERO (CRD42018095508) we systematically identified studies where CPET was used to aid in the prognostication of mortality, cardiorespiratory complications, and unplanned intensive care unit (ICU) admission in individuals undergoing non-cardiopulmonary surgery. For all included studies we extracted or calculated measures of predictive performance whilst identifying and critiquing predictive models encompassing CPET derived variables.

RESULTS

We identified 36 studies for qualitative review, from 27 of which measures of classifier performance could be calculated. We found studies to be highly heterogeneous in methodology and quality with high potential for bias and confounding. We found seven studies that presented risk prediction models for outcomes of interest. Of these, only four studies outlined a clear process of model development; assessment of discrimination and calibration were performed in only two and only one study undertook internal validation. No scores were externally validated. Systematically identified and calculated measures of test performance for CPET demonstrated mixed performance. Data was most complete for anaerobic threshold (AT) based predictions: calculated sensitivities ranged from 20-100% when used for predicting risk of mortality with high negative predictive values (96-100%). In contrast, positive predictive value (PPV) was poor (2.9-42.1%). PPV appeared to be generally higher for cardiorespiratory complications, with similar sensitivities. Similar patterns were seen for the association of Peak VO2 (sensitivity 85.7-100%, PPV 2.7-5.9%) and VE/VCO2 (Sensitivity 27.8%-100%, PPV 3.4-7.1%) with mortality.

CONCLUSIONS

In general CPET's 'rule-out' capability appears better than its ability to 'rule-in' complications. Poor PPV may reflect the frequency of complications in studied populations. Our calculated estimates of classifier performance suggest the need for a balanced interpretation of the pros and cons of CPET guided pre-operative risk stratification.

Impact Of Peak Oxygen Pulse On Patients With Chronic Obstructive Pulmonary Disease

Introduction

Patients with chronic obstructive pulmonary disease (COPD) are at an increased risk of cardiovascular comorbidities such as pulmonary hypertension or heart failure. Impaired cardiovascular function often has a significant impact on patients with COPD. Oxygen pulse (O₂P) is a surrogate for stroke volume. However, studies regarding O₂P, health-related quality of life (HRQL), and exercise capacity in patients with COPD are lacking. We aimed to confirm the association between O₂P, HRQL, exercise capacity, severe exacerbation of COPD, and other parameters in exercise testing.

Materials and methods

This study included 79 patients with COPD who underwent lung function testing, a cardiopulmonary exercise test (CPET), Borg Dyspnea Scale evaluation, completion of the St. George's Respiratory Questionnaire, and echocardiography. Cardiovascular comorbidities, COPD-related hospitalizations, and emergency room visits were recorded. We compared these parameters between two groups of patients: those with normal peak O₂P and those with impaired peak O₂P. The relationships of peak O₂P with CPET and lung function were analyzed using simple linear regression.

Results

Patients with normal peak O₂P had higher exercise capacity (peak oxygen uptake and work rate), better HRQL, lower dyspnea score, lower COPD-related hospitalizations, and higher circulatory and ventilator parameters than patients with impaired peak O₂P. According to a simple linear regression analysis, the anaerobic threshold (AT) and forced expiratory volume in one second (FEV1) showed a significant association with peak O₂P, and the Pearson correlation coefficients (Pearson's r) were 0.756 and 0.461, respectively.

Conclusion

Peak O₂P has a significant impact on exercise capacity, HRQL, dyspnea, COPD-related hospitalization, and circulatory and ventilatory functions in patients with COPD. The AT and FEV1 have strong and moderate associations with peak O₂P, respectively. Therefore, peak O₂P is an important indicator of disease severity for patients with COPD.